This invention relates to radiators for cooling a fluid medium and especially to radiators for cooling a liquid medium, such as a dielectric oil that absorbs heat from an internal heat generator. More particularly, the invention relates to a novel construction for the finned, convective-type radiator housing for the dielectric oil that circulates by convection through and around a coaxial line termination associated with RF electrical equipment.
In RF electrical equipment utilizing coaxial transmission lines, it is often desirable to use certain types of line terminations or dummy loads for absorption of RF energy. One type of termination called the wet type utilizes a liquid cooling medium to carry off the heat energy generated by the dissipation of electrical energy across a load. These line terminations include, for example, those shown and described in U.S. Pat. Nos. 2,884,603; 2,958,830; 2,973,479, 3,054,074; 3,158,823 and 3,296,560.
The line termination or dummy load is customarily designed for use with a coaxial line of specific impedance and preferably is arranged to have an input impedance, which, over a large range of frequencies, is equal to the characteristic impedance of the line. Such a load may comprise an attenuating line section including an outer sleeve conductor tapered inwardly to its rearward end and an inner conductor axially mounted within the sleeve and joined thereto at its rearward end. The inner conductor is resistive in character and may be in the form of a thin resistive coating on a ceramic core. The line termination or dummy load is enclosed in a suitable housing filled with a liquid dielectric and the tapered outer conductor is perforated or slotted to allow the liquid dielectric, serving also as a coolant, to be in continuous contact, or heat-exchanging relation, with the inner conductor. The housing containing the bath of liquid dielectric may be cooled by radiant or convective loss of heat to the atmosphere.
The dielectric liquid within the housing is preferably one having a low dielectric constant, dielectric constants of the order of about three and below being satisfactory.
The liquid cooling medium is most advantageously contained in a radiator in which the dummy load is positioned. The radiator normally has a plurality of fins formed of conductive metal, such as aluminum, and which are heated by convection from the cooling medium and radiate the heat into the surrounding atmosphere. Thus, the heat energy from the line termination is dissipated by convection to the fins and finally dissipated by radiation from the fins to the surrounding atmosphere.
In prior art radiators of this type in which the line termination is positioned with its axis horizontal or parallel to the surface on which the unit is supported, the housing has normally been of rectangular form with fins extending outwardly from the side walls and, in some instances, from the top wall. With this construction, the convective flow of the surrounding atmosphere is in paths extending upwardly from the floor across the side walls and over a portion of the top. Essentially, no flow is developed across the bottom surface of the housing. Accordingly, efficient heat transfer from the walls of the housing occurs only around a portion of the outer surface of the housing. This relatively poor heat dissipation from the available heated housing surface results in a requirement for more liquid dielectric than might otherwise be required. Also, the boxlike shape of prior art radiators of this type produce a relatively high resistance to the upward flow of the surrounding atmosphere.
In some instances, to achieve faster cooling, fans are used with the radiators to blow the atmosphere upwardly against the bottom of the housing. While this method is effective, it does not achieve optimum flow paths for the surrounding atmosphere due to the difficulty in directing the atmosphere around a rectangularly shaped body.
The radiator construction of the present invention, however, reduces the difficulties indicated above and affords other features and advantages heretofore not obtainable.